Existing optical devices for relative motion detection utilize pattern correlation techniques to determine relative motion between the device and a surface by capturing patterns characterizing the surface as the device passes over the surface (or equivalently as the surface moves past the device). Both the distance and the direction of the device movements are determined by comparing one pattern frame with the next. This technique typically detects intensity variations of shadows on surfaces; and its sensitivity and usability depends on the intensity contrast in the captured surface patterns. Relative motion sensors are used, for example, for computer pointer (e.g., mouse) control. Such pointers typically use optics to control the position of the pointer on the computer screen. More generally, optical navigation information can be used to compensate for distortion artifacts of curvilinear and rotational movement of the scanning device along a scan path.
U.S. Pat. Nos. 5,786,804; 5,578,813; 5,644,139; 6,442,725; 6,281,882; and 6,433,780 describe examples of optical mice, other hand-held navigation devices, and hand-held scanners. Typical existing devices do not function well on specular or gloss surfaces, uniform surfaces, or surfaces with shallow features, for example glass or white board. In such devices, in order to improve image contrast, specular reflections are usually blocked, and only the scattered optical radiation from the surface is captured. The surface used typically must be capable of casting shadows. Generally this means that the surface features to be observed must have dimensions in the geometric optics range for the wavelength of the optical radiation used. Accordingly, restriction to specific surface types is a typical shortcoming of current optical mouse designs.